Direct positive processes utilizing silver halide surface image emulsions containing desensitizers

ABSTRACT

IMPROVED PROCESSES ARE DISCLOSED FOR OBTAINING POSITIVE IMAGES IN AND UNFOGGED, SILVER HALIDE EMULSION WHEREIN A PHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT AND SAID EMULSION ARE IMAGEWISE-EXPOSED AND THEN EITHER (1) DEVELOPED IN A SILVER HALIDE DEVELOPER IN THE PRESENCE OF A SILVER HALIDE FOGGING AGENT OR (2) GIVEN A LIGHT FLASH DURING DEVELOPMENT IN A SILVER HALIDE DEVELOPER. IN ONE ASPECT, THE SILVER HALIDE EMULSIONS OF THIS INVENTION ARE SURFACEIMAGE EMULSIONS COMPRISING AN ELECTRON ACCEPTOR AND/OR DESENSITIZING CONCENTRATIONS OF SPECTRAL-SENSITIZING DYE AND THE GRAINS OF SAID EMULSION HAVE BEEN CHEMICALLY SENSITIZED ON THE SURFACE THEREOF TO A LEVEL LESS THAN THAT WHICH WOULD PROVIDE A SUBSTANTIAL DENSITY IN KODAK DEVELOPER DK-50 AFTER AN IMAGEWISE EXPOSURE WHEN SAID EMULSIONS ARE COATED AT A COVERAGE OF BETWEEN 300 TO 400 MG. OF SILVER PER FT.2.

United States Patent DIRECT POSITIVE PROCESSES UTILIZING SILVER HALIDE SURFACE IMAGE EMULSIONS CON- TAINING DESENSITIZERS Paul Brewster Gilman, Jr., Rochester, Ronald George Raleigh, Brockport, and Thaddeus Donald Koszelak, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, NY. No Drawing. Filed June 17, 1971, Ser. No. 154,224

Int. Cl. G03c 1/36, 15/24 US. CI. 96-64 17 Claims ABSTRACT OF THE DISCLOSURE Improved processes are disclosed for obtaining positive images in an unfogged, silver halide emulsion wherein a photographic element comprising a support and said emulsion are imagewise-exposed and then either (1) developed in a silver halide developer in the presence of a silver halide fogging agent or (2) given a light flash during development in a silver halide developer. In one aspect, the silver halide emulsions of this invention are surfaceimage emulsions comprising an electron acceptor and/or desensitizing concentrations of spectral-sensitizing dye and the grains of said emulsion have been chemically sensitized on the surface thereof to a level less than that which would provide a substantial density in Kodak Developer DK-50 after an imagewise exposure when said emulsions are coated at a coverage of between 300 to 400 mg. of silver per ft.

This invention relates to silver halide emulsions and methods of forming positive images in silver halide emulsions. In one aspect, this invention relates to unfogged silver halide emulsions which contain an electron-accepting compound or a desensitizing concentration of a spectral-sensitizing dye and which have been chemically sensitized on the surface of a level less than that which will produce substantial density in a surface developer after imagewise exposure to light. In one aspect of this invention, the silver halide emulsions are surface-image emulsions and preferably comprise silver halide grains which are substantially free of metal dopants or foreign metal ions occluded therein. In another aspect, this invention relates to an improved method for obtaining positive images wherein a silver halide element comprising the emulsion as described next above is imagewise-exposed and then the silver halide element is either given a light flash during development or developed in the presence of a silver halide fogging agent.

Processes are known in the art for making positive images in unfogged silver halide emulsions by imagewise exposure followed by fogging developers, etc. Typical processes of this type are disclosed in US. Pats. 2,497,875 by Falleson issued Feb. 21, 1950; 2,588,982 by Ives issued Mar. 11, 1952; and 2,456,953 by Knott et a1. issued Dec. 21, 1948; British Pat. 1,151,363; and Japanese Pat. 29,- 405/ 68 issued Dec. 17, 1968. Generally, the prior processes used internal-image silver halide emulsions such as emulsions made by the conversion technique of Davey et al., US. Pat. 2,592,250, emulsions made by the techniques disclosed in British Pat. 1,011,062, and the like. The above emulsions could be used to make positive images by the above techniques, but improved photographic characteristics such as higher photographic speed, lower D higher D and the like are desired to obtain acceptance of this system in many applications of photography. In still other instances, it is desirable to use developer compositions for forming positive images which are internal-image developers or contain silver halide solvents therein; many of the prior-art systems for forming 3,730,723 Patented May 1., 1973 direct-positive images in unfogged emulsions required the developing composition to be substantially free of silver halide solvents.

We have now found that photographic element containing at least one layer of unfogged surface-image silver halide emulsions, wherein the grains have been chemically sensitized on the surface thereof to a level less than that which would provide a substantial density in Kodak DK- 50 Developer for 6 minutes at 27 C. after imagewise exposure and wherein the emulsion contains an electronaccepting compound and/ or a desensitizing level of a spectral-sensitizing dye, can be imagewise-exposed and processed in a fogging developer or flashed with an overall exposure of light during development in a silver halide developer to provide a positive image. This discovery was quite unexpected since one skilled in the art generally avoided conditions or steps where the surface of the emulsion would be chemically sensitized before the imagewise exposure when it was to be used in a process to form a reversal positive image, and in many instances internalimage emulsions were employed.

In one embodiment of this invention, an improved proc ess is provided for making reversal images, the improvement comprising using an unfogged silver halide emulsion containing an electron-accepting compound and/or a desensitizing level of a spectral-sensitizing dye wherein said silver halide grains have been chemically sensitized to a level below that which would produce a density of 0.25 and preferably less than 0.1 when imagewise-exposed and developed in Kodak DK-SO Developer and to provide a density of at least 0.3 in a silver halide emulsion not containing an organic electron acceptor and/ or a desensitizing level of a spectral-sensitizing dye of the same grain size and halide composition when exposed and developed in Kodak DK-SO Developer, provided the emulsion is coated at a coverage of between about 300 mg. to about 400 mg. Ag/ftf As a highly preferred embodiment according to this invention, the useful silver halide emulsions can be characterized as being a silver halide composition wherein (1) the halide is predominantly bromide, (2) the unexposed emulsion when coated on a film support at a coverage between about to 400 mg. Ag/ft. and processed in a surface developer such as Kodak DK50 will have a density of less than 0.2, and (3) when the emulsions are coated and exposed as described as next above and then processed in a fogging developer as described in Ives, US. Pat. 2,563,785, the emulsion will have a AD or (D -D of greater than 1.0..

In one preferred embodiment, the emulsions having the characteristics next above are processed after imagewise exposure in a silver halide developer composition in the presence of a hydrazine fogging agent.

In another preferred embodiment, the emulsions having the characteristics above are processed after imagewise exposure in a silver halide developer composition in the presence of a reactive N-substituted, cycloammonium quaternary salt.

In still another embodiment, the silver halide emulsions of this invention are processed after imagewise exposure with an over-all light flash during development in a silver halide developer.

In another embodiment, the emulsions of this invention can be used to provide improved image transfer systems and processes for forming a transfer image. The emulsions of this invention can comprise at least one layer in an image transfer film unit which additionally comprises an image-receiving layer and a processing composition which can be discharged to facilitate development of the silver halide emulsion by passing the unit through a pair of juxtaposed pressure-applying members. Preferably, a selective fogging agent is located in the film unit whereby it will contact said silver halide upon discharge of the processing composition, such as in one layer of the element or in a rupturable pod.

Generally, the suraceimage emulsions of this invention can be any silver halide composition wherein the light sensitivity is predominantly on the surface of the grain such that the latent image can be developed in surface-image silver halide developing compositions which are substantially free of silver halide solvents. Preferably, the halide of the silver halide is predominantly bromide and the halide comprises less than 30 mole percent iodide. In certain preferred embodiments, the silver halide emulsions comprise silver halide grains which are substantially free of metallic dopants or foreign metal ions. The term foreign metal ion is understood to mean metal ion other than a silver ion and the term metallic dopant is understood to mean metals in their metallic state, metal salts and metal complexes exclusive of silver halides. In one preferred embodiment, the surface-sensitive silver halide emulsions, when examined according to normal photographic testing techniques by coating a test portion of the emulsion on a transparent support, exposing to a light-intensity scale for a fixed time between 1 10- and 1 second, and developing for about 5 minutes at 65 F. in Developer X below (a surface-type developer), have a maximum density at least two times the maximum density of an identical test portion which has been exposed in the same way, bleached for 5 minutes in an aqueous 0.3 percent potassium ferricyanide solution at 65 F. and developed for 6 minutes at 68 F. in Developer Y below (an internal-type developer). Preferably, the maximum density in Developer X is at least 0.5 density unit greater than the maximum density obtained next above in Developer Y and/or the grains of said emulsion have a ratio of total sensitivity to internal sensitivity of greater than 5.

DEVELOPER X G. N-methyl-p-aminophenol sulfate 2.5 Ascorbic acid 10.0 Potassium metaborate 35.0 Potassium bromide 1.0 Water to 1 liter. pH of 9.6.

DEVELOPER Y G. N-methyl-p-aminophenol sulfate 2.0 Sodium sulfite, desiccated 90.0 Hydroquinone 8.0 Sodium carbonate, monohydrate 52.5 Potassium bromide 5.0 Sodium thiosulfate 10.0

Water to 1 liter.

The silver halides used in the present invention are unfogged. Such emulsions as used in the present photographic elements contain only minimal developable surface latent images wherein processing for 5 minutes at 27 C. in Kodak Developer DK-SO will provide a density of less than 0.4 and preferably less than 0.25.

The surface of the grains of the emulsions of this invention is generally chemically sensitized to a level below that which would produce substantial density (i.e., a density of less than 0.25) in a surface developer such as Kodak Developer DK-50 after exposure when coated together with a desensitizing level of a sensitizing dye or an electron acceptor at a coverage of between about 300 to 400 mg. Ag/ft. Preferably, the emulsion is sensitized to a level which would provide at least a 0.3 log E speed increase in the absence of an electron acceptor or sensitizing dye when compared to a primitive unsensitized silver halide emulsion of similar grain size distribution, composition and the like.

By chemical sensitization, I mean senstization of the type described by Antoine Hautot and Henri Saubenier in Science et Industries Photographiques, Vol. XXVIII, January 1957, pages l-23, and January 1957, pages 5765. Such chemical sensitization includes three major classes, viz, gold or noble metal sensitization, sulfur sensitization such as by a labile sulfur compound, and reduction sensitization, i.e., treatment of the silver halide with a strong reducing agent which does not fog appreciably the silver halide, but introduces small specks of metallic silver into the silver halide crystal or grain. In certain embodiments, the optimum sensitization will vary with developer composition, e.g., smaller amounts of chemical sensitization are used when the emulsion is to be developed in p-phenylenediamine-containing developing compositions, iodidecontaining developing compositions and the like.

The silver halide grains can be chemically sensitized by any of the accepted procedures. The silver halide grains can be digested with naturally active gelatin, sulfur compounds can be added, such as those described in U.S. Pats. 1,574,944 by Sheppard issued Mar. 2, 1926, 1,623,499 by Sheppard et al. issued Apr. 5, 1927, and 2,410,689 by Sheppard issued Nov. 5, 1946, or selenium compounds can be used, such as those described in U.S. Pats. 3,297,447 by McVeigh, 3,297,446 by Dunn, and the like.

The silver halide grains can also be treated with salts of the noble metals, such as ruthenium, palladium and platinum. Representative compounds are ammonium chloropalladate, potassium chloroplatinate and sodium chloropalladite, which are used for sensitizing in amounts below that which produces any substantial fog inhibition, as described in Smith and Trivelli, U.S. Pat. 2,448,060 issued Aug. 31, 1948, and as antifoggants in higher amounts, as described in Trivelli and Smith, U.S. Pats. 2,566,245 issued Aug. 28, 1951, and 2,566,263 issued Aug. 28, 1951.

The silver halide grains can also be chemically sensitized with gold salts as described in U.S. Pats. 2,399,083 by Waller et al. issued Apr. 23, 1946, and 2,642,361 by Damschroder et al. issued June 16, 1953. Suitable compounds are potassium chloroaurite, potassium aurithiocyanate, potassium chloroaurate, auric trichloride and 2- aurosulfobenzothiazole methochloride.

The silver halide grains can also be chemically sensitized with reducing agents, such as stannous salts (Carroll, U.S. Pat. 2,487,850 issued Nov. 15, 1949), polyamines, such as diethylene triamine (Lowe et al., U.S. Pat. 2,518,698 issued Aug. 15, 1950), polyamines, such as spermine (Lowe et al., U.S. Pat. 2,521,925 issued Sept. 12, 1950), or bis (pi-aminoethyDsulfide and its watersoluble salts (Lowe et al., U.S. Pat. 2,521,926 issued Sept. 12, 1950).

The silver halide grains can also be spectrally sensitized with cyanine and merocyanine dyes, such as those described in U.S. Pats. 1,846,301 and 1,846,302 both issued Febr. 23, 1932, and 1,942,854 issued Jan. 9, 1934, all by Brooker; 1,990,507 by White issued Febr. 12, 1935; 2,112,140 issued Mar. 22, 1938, 2,165,338 issued July 11, 1939, 2,493,747 issued 1 an. 10, 1950, and 2,739,964 issued Mar. 27, 1956, all by Brooker et al.; 2,493,748 by Brooker et al. issued Jan. 10, 1950; 2,503,776 issued Apr. 11, 1950, and 2,519,001 issued Aug. 15, 1950, both by Sprague; 2,666,761 by Heseltine et al. issued Jan. 19, 1954; 2,734,- 900 by Heseltine issued Febr. 14, 1956; and 2,739,149 by Van Lare issued Mar. 20, 1956; and Kodak Limited British Pat. 450,958 accepted July 15, 1936.

In certain embodiments where the surface of the grains has been chemically sensitized at the low end of the specified range, it is desirable to incorporate iodide-releasing compounds in the silver halide element or to use a developer containing iodide ions to obtain certain desired image characteristics. However, as the level of chemical sensitization is increased, the use of the iodide-releasing compounds or iodide in the developer or emulsion becomes less desirable.

'In accordance with this invention, a simple exposure and development process can be used to form a positive image. In one embodiment, a photographic element comprising at least one layer of a silver halide composition as described above can be imagewise-exposed and then developed in the presence of a fogging agent in a silver halide developer. In another embodiment, the element can be given a flash over-all exposure during development to provide a positive image.

The developing compositions which can be used in the processes of the present invention can be either totalimage developing compositions which contain silver halide solvents or surface-image developing compositions. In certain preferred embodiments, however, the developing compositions utilized are surface developers.

It is understood that the term surface developer encompasses those developers which Will reveal the surface latent inmage on a silver halide grain, but will not reveal substantial internal latent image in an internal imageforming emulsion, and conditions generally used develop a surface-sensitive silver halide emulsion. The surface developers can generally utilize any of the silver halide developing agents or reducing agents, but the developing bath or composition is generally substantially free of a silver halide solvent (such as water-soluble thiocyanates, water-soluble thioethers, thiosulfates, ammonia and the like) which will crack or dissolve the grain to reveal substantial internal image. Low amounts of excess halide are sometimes desirable in the developer or incorporated in the emulsion as halide-releasing compounds, but high amounts are generally avoided to prevent substantial cracking of the grain, especially with respect to iodidereleasing compounds.

Typical silver halide developing agents which can be used in the developing compositions of this invention include hydroquinones, catechols, aminophenols, 3-pyrazolidones, ascorbic acid and its derivatives, reductones, phenylenediamines and the like or combinations thereof. The developing agents can be incorporated in the photographic elements wherein they are brought in contact with the silver halide after imagewise exposure; however, in certain embodiments they are preferably employed in the developing bath.

The developing compositions used in the process of this invention can also contain certain antifoggants and development restrainers, or optionally they can be incorporated in layers of the photographic element. Typical useful antifoggants include nitrobenzimidazoles, benzothiazoles such as S-nitrobenzothiazole and S-methylbenzothiazole, heterocyclic thiones such as 1-methyl-2-tetrazoline-S-thione, aromatic and aliphatic mercapto compounds, and the like.

The emulsions of this invention comprise electron acceptors, which are referred to in some documents as desensitizers, or desensitizing concentrations of spectral-sensitizing dyes. The concentrations of the electron acceptors or sensitizing dyes will vary with silver halide composition, average grain size, distribution of grain size, etc. In certain preferred embodiments, very good results are obtained when the electron acceptors or sensitizing dyes are added to monodispersed silver halide emulsions. In another preferred embodiment, at least 300 mg., and preferably at least 400 mg., of a sensitizing dye per silver mole are used in a monodispersed silver halide emulsion of about 0.2 micron diameter grains. In those embodiments where the combination of an electron acceptor and a spectral-sensitizing dye is used, the level of the spectralsensitizing dye is generally less than 200 mg. of the dye per silver mole.

The electron acceptors useful in the emulsion combinations of this invention are those compounds having a reduction potential or cathodic halfWa-ve potential (B more positive than -1.0, i.e., -0.40, 0.2 and the like. Compounds of this type have been referred to in some prior-art disclosures as desensitizers. Typical useful electron acceptors also have an oxidation potential or anodic halfwave potential more positive than +0.4 and preferably more positive than +1.0.

The halfwave potential measurements can be made as described in Illingsworth, US. Pat. 3,501,307 issued Mar. 17, 1970, for example, the cathodic measurements can be made with a 1 10 molar solution of the electron acceptor in a solvent, for example, methanol which is 0.05 molar in lithium chloride using a dropping mercury electrode with the polarographic halfwave potential for the most positive cathodic wave being designated B In the measurement, the reference electrode can be an aqueous silver-silver chloride (saturated potassium chloride) electrode at 20 C. Electrochemical measurements of this type are known in the art and are described in New Instrumental Methods in Electrochemistry, by Delahay, Interscience Publishers, New York, N.Y., 1954; P0- larography, by Kolthoff and Lingane, 2nd edition, Interscience Publishers, New York, N.Y., 1952; Analytical Chemistry, 36, 2426 (1964), by Elving; and Analytical Chemistry, 30, 1576 (1958), by Adams. Plus and minus signs are according to IUPAC (International Union of Pure and Applied Chemistry) Stockhold Convention, 1953.

In a preferred embodiment of this invention, the desensltizers are methine dyes, generally referred to as monomethine and/ or polymethine dyes. Generally, these methine dyes include those which are useful in direct-positive silver halide emulsions as electron acceptors.

In certain preferred embodiments, the useful polyrnethine dyes of this invention can be characterized as containing at least one desensitizing nucleus. As used herein and in the appended claims, desensitizing nucleus refers to those nuclei which, when converted to a symmetrical carbocyanine dye and added to a gelatin silver chlorobromide emulsion containing 40 mole percent chloride and 60 mole percent bromide, at a concentration of from 0.01 to 1.0 gram dye per mole of silver, caused by electron trapping at least about an percent loss in the blue speed of the emulsion when sensitometrically exposed and developed 3 minutes in Kodak Developer D19 at room temperature. Advantageously, the desensitizing nuclei are those which, when converted to a symmetrical carbocyanine dye and tested as just described, essentially com pletely desensitize the test emulsion to blue radiation (i.e., cause a loss of more than about to percent of speed to blue radiation).

An especially useful class of electron accepting compounds which can be used in the photographic silver halide emulsions of this invention is cyanine dyes, particularly imidazoquinoxaline dyes, such as described in Brooker et al., US. Pat. 3,431,111 issued Mar. 4, 1969. Very good results are obtained with cyanine dyes containing an indole nucleus aromatically substituted in the 2 position, i.e., a cyanine dye containing a 2-aromatically substituted indole nucleus such as disclosed in US. Pat. 3,314,796 issued Apr. 18, 1967. One useful class of spectral-sensitizing, electron acceptors is the bis-(l-alkyl- 2 phenylindole 3) trimethine cyanine described by Coenen et al., U.S. Pat. 2,930,694 issued Mar. 29, 1960. Another useful class of dimethine cyanine dyes of this type is described in British Pat. 970,601.

Still other classes of useful spectral-sensitizing electron acceptors are the cyanine and merocyanine dyes in which at least one nucleus and preferably two nuclei contain desensitizing substituents such as N0 e.g., 3,3-diethyl- 6,6'-dinitrothiacarbocyanine chloride, as shown in British Pat. 723,019.

The electron acceptors or desensitizers can be used in the photographic silver halide emulsions of this invention in widely varying concentrations. However, such compounds are preferably employed at concentrations in the range of about 10 milligrams to about 2 grams of the compound per mole of silver halide. Specific examples of suitable polymethine electron acceptors include the following:

(1 l, l'-dimethyl-2,2'-diphenyl-3,3'-indolocarbocyanine bromide TCH=CHOH l \N/ Ph Ph g life life Br (2) 2,2'-di-p-methoxyphenyl-1, l'dimethyl-3 ,3 -indolocarbocyanine bromide TCH=CHCH (3 1,1'-dimethyl-2,2, 8-triphenyl-3,3'-indolocarbocyanine perchlorate CH=C Eli-CT N P h P h g Il /Io life (4) 1,l',3,3'-tetraethylimidazo [4,5-b1quinoxalinocarbocyanine chloride Additional examples include phenosafranine,

pinacryptol yellow,

5-m-nitrobenzylidenerhodanine,

S-ethyl-5-m-nitrobenzylidenerhodanine,

3-ethyl-5- 2,4-dinitrobenzylidene rhodanine,

5-o-nitrobenzylidene-3-phenylrhodanine,

1',3-diethyl-6-nitrothia-2'-cyanine iodide,

4-r1itro-6-chlorobenzotriazole,

3,3'-diethyl-6,6'-dinitro-9-phenylthiacarbocyanine iodide,

2-(p-dimethylaminophenyliminomethyl)benzothiazole ethoethyl sulfate,

crystal violet,

3,3-diethyl-6,6'-dinitrothiacarbocyanine ethyl sulfate,

1',3-diethyl-6-nitrothia-2'-cyanine iodide,

l,3-diamino-S-methylphenazinium chloride,

4-nitro-6-chlorobenzotriazole,

3,3'-di-p-nitrobenzylthiacarbocyanine bromide,

3,3'-di-p-nitrophenylthiacarbocyanine iodide,

3,3'-di-o-nitrophenylthiacarbocyanine perchlorate,

3,3-dimethyl-9-trifluoromethylthiacarbocyanine iodide,

9-(2,4-dinitrophenylmercapto)-3,3-diethylthiacarbocyanine iodide,

bis (4,6-diphenylpyryl-2 trimethincyanine perchlorate,

anhydro-2-p-dimethylaminophenyliminomethyl-6-nitro- 3-(4-sulfobutyl)benzothiazolium hydroxide,

1- (2-b enzothiazolyl -2- (p-dimethylaminostyryl -4,6-

diphenylpyridinium iodide,

2,3,S-triphenyl-2H-tetrazolium chloride,

2-(4-iodopheny1)-3-(4-nitrophenb l)-5-phenyltetrazolium chloride,

1-methyl-8-nitroquinolinium methyl sulfate, 3,6-bis [4- 3-ethyl-2-benzothiazolinylidene -2-butenylidene]-1,2,4,5-cyclohexanetetrone and the like.

The organic compounds useful herein may also serve as spectral sensitizers in the visible region of the electromagnetic spectrum. An especially useful class of spectralsensitizing electron acceptor is trimethine cyanine dye containing a 2-aromatically substituted indole nucleus attached by the 3-carbon atom thereof to the methine chain. Dyes of this type are described by Coenen et al. in US. Pat. 2,930,694 issued Mar. 29, 1960, and British Pat. 970,601 (and corresponding Belgian Pat. 630,911). A preferred class of spectrally sensitizing electron acceptors is dye containing an imidazo[4,5-b]quinoxalinium salt moiety, such as disclosed in Brooker and Van Lare, Belgian Pat. 660,253 issued Mar. 15, 1965. In these dyes, the imidazo[4,5-b]quin0xaline nucleus is attached, through the 2-carbon atom thereof, to the methine chain.

Another class of highly useful polymethine dyes is that having the following formula:

Formula 1 R2 wherein R R and R each represents a value selected from those given for R R and R A typical specific useful dye of this class is 1,l,3,3,3,3-hexamethylpyrrolo- [2,3-b]pyridocarbocyanine salt (e.g., perchlorate).

One useful group of trimethine cyanine dyes having 2- aromatically substituted indole nuclei has the following general formula:

Formula 2 C H: C H- C Y gm] li/O wherein X has the meaning given above; A represents an aryl substituent, such as phenyl; R and R each represents an alcohol radical, e.g., an alkyl substituent (including substituted alkyl) and preferably containing from about 1 to 8 carbon atoms, such as methyl, ethyl, propyl, butyl or octyl, or sulfoalkyl such as sulfopropyl or sulfobutyl, sulfatoalkyl such as sulfatopropyl or sulfatobutyl, or carboxyalkyl such as carboxyethyl or carboxybutyl; and Y represents a substituent selected from the group consisting of a hydrogen atom, an aryl group, such as phenyl, and alkyl (e.g., methyl, ethyl, propyl or butyl) or alkoxy (e.g., methoxy, ethoxy or propoxy) substituted phenyl groups, or a heterocyclic aromatic group, such as thiophene radical.

Symmetrical imidazo[4,5-b]quinoxaline trimethine cyanine dyes, wherein each nucleus is attached through the Z-carbon atom thereof to the methine chain, are useful in the practice of this invention. Typical of such dyes are those having the following general formula:

Formula 3 Ilh In N N N I G=CHCH=OHC 1k l 'lio N Xe wherein X has the meaning given above; and R R R and R each represents a substituent such as alkyl, e.g., methyl, ethyl, propyl or butyl. Reference is made to Brooker and Van Lare, Belgian Pat. 660,253 issued Mar. 15, 1965, for other classes and specific examples of dyes containing an imidazo[4,5-b]quinoxaline nucleus which are useful herein.

' The sensitizing dyes useful in this invention generally include all dyes known to be useful in spectrally sensitizing, silver halide emulsions, and preferably are those characterized as methine or polymethine dyes. According to the present invention, the respective dyes are used in desensitizing concentrations, i.e., a greater amount than that necessary for obtaining an optimum sensitizing effect with an emulsion which has been only surface-sensitized. In one preferred embodiment, the sensitizing dyes are used in concentrations which generally desensitize a surface-sensitive emulsion. In this embodiment, the sensitizing dyes are used at a concentration above that which will lower the blue-speed sensitivity of a sulfurand goldsurface-sensitized, silver bromoiodide (6 mole percent iodide) emulsion at least 0.3 log B when developed in a surface developer such as Kodak D-19.

The dyes which can be used in the emulsion combinations of this invention in desensitizing concentrations are characterized as being spectral-sensitizing dyes for silver halide emulsions including the ultraviolet, visible and infrared regions of the spectrum. The dyes are further characterized as having a reduction potential or cathodic halfwave potential less positive than -l.0, i.e., such as cathodic halfwave potentials, of 1.5, 2.0, etc. Typical useful sensitizing dyes according to this invention also have an oxidation potential or anodic halfwave potential more positive than +0.4 and preferably more positive than f+0.55.

Typical useful classes or dyes which can be used according to this invention include the methine dyes such as the cyanines, isocyanines, pseudocyanines, hemicyanines, merocyanines, oxanols, azacyanines and the like. Generally, any dye which can be used to sensitize spectrally a silver halide emulsion at low concentrations can now be used in high concentrations when used in the reversal systems according to this invention.

The silver halide emulsions of this invention can generally be developed in any silver halide developing composition in the presence of a fogging agent to provide good positive images. The fogging agent can be incorporated in at least one layer of the silver halide element, which layer is in water-permeable association with the silver halide emulsion, or it can be contacted with said silver halide emulsion by a separate bath or simultaneously with the developer composition by incorporating the fogging agent into the fogging agent into the developer composition. Generally, the useful fogging agents of this invention are those which provide nucleation or fog specks which initiate development of the silver halide in the unexposed areas before initiating substantial development in the exposed areas. Compounds of this type are generally not practical developing agents by themselves for silver halides and are referred to as selective fogging agents; in some documents they have been referred to generally as silver halide fogging agents or nucleating agents. Typical useful selective fogging agents include hydrazine compounds, reactive N-substituted cycloammonium salts and the like.

In one preferred embodiment of the invention, hydrazines are used as the fogging agent, such as the compounds disclosed in US. Pats. 2,588,982 by Ives issued Mar. 11, 1952, and 3,227,552 by Whitmore issued Jan. 4, 1966.

In another preferred embodiment, the fogging agents are reactive N-substituted cycloammonium quaternary salts. Typical useful fogging agents of this type are disclosed in US. Ser. Nos. 28,041 by Lincoln et al. filed Apr. 13, 1970, 85,706 by Kurtz et: al. filed Oct. 30, 1970, and 85,709 by Kurtz et al. filed Oct. 30, 1970, which are incorporated herein by reference. Generally, those compounds can be represented by the formula:

(A) Z represents the atoms necessary to complete a heterocyclic nucleus containing a heterocyclic ring of 5 to 6 atoms including the quaternary nitrogen atom, with the additional atoms of said heterocyclic ring being selected from carbon, nitrogen, oxygen, sulfur and selenium;

(B) jrepresents a positive integer of from 1 to 2;

(C) a represents a positive integer of from 2 to 6;

(D) X represents an acid anion;

(E) R represents a member selected from:

( 1) a formyl radical, (2) a radical having the formula:

wherein each of T and T when taken alone, represents a member selected from an alkoxy radical and an alkylthio radical, and T and T when taken together, represent the atoms necessary to complete a cyclic radical selected from cyclic oxyacetals and cyclic thioacetals having from 5 to 6 atoms in the heterocyclic acetal ring, and (3) a l-hydrazonoalkyl radical; and (F) R represents either a hydrogen atom, an alkyl radical, an aralkyl radical, an alkylthio radical or an aryl radical such as phenyl and naphthyl, and including substituted aryl radicals.

In certain preferred embodiments of this invention, the N-substituted, cycloammonium quaternary salts are those which contain N-substituted alkyl radicals having the terminal carbon atom substituted with a hydrazono radical, an acyl radical such as a formyl radical, an acetyl radical or a benzoyl radical, and those which have a dihydroaromatic ring nucleus such as, for example, a dihydropyridinium nucleus.

Generally, the fogging agents can be incorporated in at least one layer of the photographic element in waterpermeable association with the silver halide emulsion or they can be contacted with the emulsion before or during development such as by a pre-bath or incorporating the fogging agent in the developer composition; how ever, the fogging agents are preferably located in at least one layer of the element and in a highly preferred embodiment they are located in the silver halide emulsion layer. Concentrations of from about 75 to about 1500 mg. of the subject fogging agents per mole of silver in the silver halide emulsion are useful, with from about to about 1200 mg. of said compounds or agents per mole of silver being preferred. These ratios are accord- 11 ing to conventional practice, however, and with either particular reversal emulsions, fogging compounds of varying chemical activity, or varying processing conditions, more widely varying fogging agent concentrations can be advantageously used.

Typical useful selective fogging agents include 2-methyl-3-[3-(p sulfophenylhydrazone) propyl1benzothiazolium bromide,

hydrazine dihydrochloride,

phenylhydrazine hydrochloride,

p-methyl sulfonamide ethyl phenyl hydrazine,

formyl-4-methyl phenyl hydrazide,

3- (2-formylethyl -2-methylbenzothiazolium bromide,

3-(2-acetylethyl)-2-benzylbenzothiazolium bromide,

3-(2-acetylethyl)-2-benzylbenzoselenazolium bromide,

1,2-dihydro-3-methyl-4-phenyl pyrido [2,1-b3benzothiazolium bromide,

4,4'-ethylene bis( 1,2-dihydro-3-methylpyrido[2,1-b]

benzothiazolium bromide),

2-methyl-3-[ (3-p-nitrophenylhydrazono propyl] naphtho[2,1-d]thiazolium iodide, and the like.

The silver halide emulsions of this invention can be made by any of the precipitation and ripening procedures used for making silver halide grains. Typical procedures include single-jet procedures, double-jet procedures, procedures utilizing automatic proportional control means to maintain specified pAg and pH, procedures using ripening agents such as thiocyanates, thioethers and/or ammonia, procedures utilizing an increase in flow rates as disclosed in WllgIlS, U.S. Ser. No. 11,838 filed Feb. 16, 1970, now abandoned, hot nucleation procedures as disclosed in Musliner, U.S. Ser. No. 31,351 filed Apr. 23, 1970, and the like.

The silver halide compositions made for use in the systems of this invention are preferably monodispersed, and in some embodiments are preferably large-grain emulsions made according to Wilgus, U.S. Ser. No. 11,838, which is incorporated herein by reference. The monodispersed emulsions are those which comprise silver halide grains having a substantially uniform diameter. Generally, in such emulsions, no more than about 5%, by weight, of the silver halide grains smaller than the mean grain size and/or no more than about 5%, by number, of the silver halide grains larger than the mean grain size vary in diameter from the mean grain diameter by more than about 40%. Preferred photographic emulsions of this invention comprise silver halide grains, at least 95%, by weight, of said grains having a diameter which is within 40%, preferably within about 30%, of the mean grain diameter. Mean grain diameter, i.e., average grain size, can be determined using conventional methods, e.g., such as projective area as shown in an article by Trivelli and Smith entitled Empirical Relations Between sensitometric and Size-Frequency Characteristics in Photographic Emulsion Series in The Photographic Journal, Vol. LXXIX, 1939, pp. 330-338. The aforementioned uniform size distribution of silver halide grains is a characteristic of the grains in monodispersed photographic silver halide emulsions. Silver halide grains having a narrow size distribution can be obtained by controlling the conditions at which the silver halide grains are prepared using a double-run procedure. In such a procedure, the silver halide grains are prepared by simultaneously running an aqueous solution of a water-soluble silver salt, for example, silver nitrate, and a Water-soluble halide, for example, an alkali metal halide such as potassium bromide, into a rapidly agitated aqueous solution of a silver halide peptizer, preferably gelatin, a gelatin derivative or some other protein peptizer. The pH and the pAg employed in this type of procedure are interrelated. For example, changing one while maintaining the other constant at a given temperature can change the size frequency distribution of the silver halide grains which are formed. However, generally the temperature is about 30 to about 90 C., the pH is up to about 9, prefer- 12 ably 4 or less, and the pAg is up to about 9.8. Suitable methods for preparing photographic silver halide emulsions having the required uniform particle size are disclosed in an article entitled Ia: Properties of Photographic Emulsion Grains, by Klein and Moisar, The Journal of Photographic Science, Vol. 12, 1964, pp. 242- 251; an article entitled The Spectral Sensitization of Silver Bromide Emulsions on Difierent Crystallographic Faces, by Markocki, The Journal of Photographic Science, Vol. 13, 1965, pp. -89; an article entitled Studies on Silver Bromide Sols, Part I. The Formation and Aging of Monodispersed Silver Bromide Sols, by Ottewill and Woodbridge, The Journal of Photographic Science, Vol. 13, 1965, pp. 98-103; and an article entitled Studies on Silver Bromide Sols, Part II. The effect of Additives on the S01 Particles, by Ottewill and Woodbridge, The Journal of Photographic Science, Vol. 13, 1965, pp. 104-107.

The photographic emulsions and elements described in the practice of this invention can contain various colloids alone or in combination as vehicles, binding agents and various layers. Suitable hydrophilic materials include both naturally occurring substances such as proteins, for example, gelatin, gelatin derivatives, cellulose derivatives, polysaccharides such as dextran, gum arabic and the like; and synthetic polymeric substances such as water-soluble polyvinyl compounds like poly(vinylpyrrolidone), acrylamide polymers and the like.

The described photographic emulsion layers and other layers of a photographic element employed in the practice of this invention can also contain, alone or in combination with hydrophilic, Water-permeable colloids, other synthetic polymeric compounds such as dispersed vinyl compounds such as in latex form and particularly those which increase the dimensional stability of the photographic materials. Suitable synthetic polymers include those described, for example, in U.S. Pat. 3,142,568 by Nottorf issued July 28, 1964; 3,193,386 by White issued July 6, 1965; 3,062,674 by Houck et al. issued Nov. 6, 1962; 3,220,844 by Houck et al. issued Nov. 30, 1965; 3,287,289 by Ream et al. issued Nov. 22, 1966; and 3,411,911 by Dykstra issued Nov. 19, 1968; particularly effective are those water-insoluble polymers or latex copolymers of alkyl acrylates and methacrylates, acrylic acid, sulfoalkyl acrylates or methacrylates, those which have cross-linking sites which facilitate hardening or curing, those having recurring sulfobetaine units as described in Canadian Pat. 774,- 054 by Dykstra, and those described in U.S. Pat. 3,488,708 by Smith issued Jan. 6, 1970.

The photographic layers and other layers of a photographic element employed and described herein can be coated on a wide variety of supports. Typical supports include cellulose nitrate film, cellulose ester film, poly(vinyl acetal) film, polystyrene film, poly( ethylene terephthalate) film, polycarbonate film and related films or resinous materials, as well as glass, paper, metal and the like. Typically, a flexible support is employed, especially a paper support, which can be partially acetylated or coated with baryta and/ or an alpha-olefin polymer, particularly a polymer of an alpha-olefin containing 2 to 10 carbon atoms such as polyethylene, polypropylene, ethylenebutene copolymers and the like.

This invention may be used with elements designed for colloid transfer processes such as described in U.S. Pat. 2,716,059 by Yutzy et al.; silver salt diffusion transfer processes such as described in U.S. Pats. 2,352,014 by Rott, 2,543,181 by Land, 3,020,155 by Yackel et al. and 2,861,- 885 by Land; color image transfer processes such as described in U.S. :Pats. 3,087,817, 3,185,567 and 2,983,606 by Rogers, 3,253,915 by Weyerts et al., 3,277,550 by Whitmore et al., 3,227,551 by Barr et al., 3,227,552 by Whitmore and 3,415,644, 3,415,645 and 3,415,646 by Land, and U.S. Ser. Nos. 27,990 and 27,991, both filed Apr. 13, 1970; and imibition transfer processes as described in U.S. 'Pat. 2,882,156 by Minsk.

This invention may be used with elements designed for color photography, for example, elements containing colorforming couplers such as those described in U.S. Pats. 2,376,679 by Frohlich et al., 2,322,027 by Jelley et al., 2,801,171 by Fierke et al., 2,698,794 by Godowsky, 3,227,- 554 by Barr et al. and 3,046,129 by Graham et 211.; or elements to be developed in solutions containing color-forming couplers such as those described in U.S. Pats. 2,252,- 718 by Mannes et al., 2,592,243 by Carroll et al. and 2,950,970 by Schwan et a1.; and in false-sensitized color materials such as those described in U.S. Pat. 2,763,549 by Hanson.

The invention can be further illustrated by the following examples of preferred embodiments thereof.

EXAMPLE 1 A monodispersed silver iodobromide emulsion with 0.2g

cubic grains is sulfur-plus-gold-sensitized with 33 mg. of

sodium thiosulfate/ silver mole and 6.6 mg. of potassium chloroaurate/ silver mole which is heated for 60 minutes at 65 C. to product a 1.0 log E speed increase over the starting emulsion, then diluted and spectrally sensitized as follows:

(1) To 23.5 g. of emulsion (0.14 mole) are added 34.8 g. of a 10% gelatin solution, 64.7 g. distilled water, 1.0 g. of a 12% saponin solution and 16.0 g. of solvent plus dye which is held for 15 minutes at 40 C.

(2) A series of coatings containing 100, 200, 400 and 800 mg. of 1,3-diethyl-1-methyl-2'-phenylimidazo[4,5-b] quinoxolino 3' inodolcarbocyanine iodide (E =0.64; E =greater than 'f+1.0) per mole of silver are made.

(3) When these coatings are exposed in a modified Bausch and Lomb spectrograph for W second at 0.5 mm. and processed for 6 minutes in Developer A (a total developer) at 15 C., the coating with the 800 mg./mole of Dye A shows a high-speed reversal image in both the blue and spectrally sensitized region (520-500 mm. The coatings with lower levels of dye show a weak negative image and no fog in the unexposed areas. The presence of Dye A thus contributes to both the loss of negative latent-image formation and the development of fog in the unexposed areas. Increasing the time of processing in Developer A leads to higher maximum densities (greater than 1.5 with a loss in reversal speed over the 6-minute development.

A series of dye coatings similar to Example 1 are coated except phenosafranine (E =0.54; E =1+ 1.00) is substituted for Dye A. When 400 mg. of phenosafranine/ silver mole are added to the silver halide emulsion, a highspeed reversal is observed (500-540 nm.).

EXAMPLE 3 The coating containing the 400 mg. of Dye A/mole of silver as prepared in Example 1 is exposed and processed in a fogging developer having the following composition:

G. Hydroquinone -2--- 10.0 Elon 5.0 Na SO 75.0 NaO H 10.5 S-methylbenzotriazole .02 p-[fl (Methylsulfonamido)ethyl]phenyl hydrazine hydrochloride 2.0

G. Diglycolic acid 13.4 Na PO 75.0 Water to 1 liter. pH=l1.2.

A high-speed, direct-positive image is obtained after development for 3 minutes at 21 C.

EXAMPLE 4 A 0.2g. silver bromoiodide emulsion (6 mole percent iodide), which has been reduction-sensitized with 2 mg. of stannous chloride/silver mole, is imbibed for 1 minute in a solution of Dye A containing 0.5 mg. of dye per milliliter of a 50/50 mixture of methanol and water. After drying, the coating is exposed on a Bausch and Lomb wedge spectrograph for /2 second at 0.5 mm. It is then processed for 5 minutes at 27 C. in the fogging developer of Example 3 to produce a very high-quality reversal image with sensitivity extending from 400 to 620 nm.

EXAMPLE 5 A coarse-grained silver iodobromide X-ray-type emulsion prepared by the double-jet technique is reductionsensitized as described in Example 4 and coated with a desensitizing level of anhydro-3-ethyl-9-methy1-3'-(sulfobutyl)thiacarbocyanine hydroxide (Dye B) (E =-1.29; E =+.73) at 800 mg./mole. When this coating is exposed on a Bausch and Lomb wedge spectrograph at of a second and a slit width of 0.5 mm. and processed in the fogging developer of Example 3 for 1 minute at 27 C., a high-speed, high-density, direct-positive image is obtained with spectral sensitivity from 360 to 640 nm.

EXAMPLE 6 A single-run bromoidide of coarse-grain size is sulfurplus-gold-sensitized by adding 2.2 mg. of sodium thiosulfate/silver mole and 0/.84 mg. of potassium chloroaurate/silver mole and heated for 10 minutes at 65 C., then coated with mg./ silver mole of 1,1-diethyl-2,2'- cyanine chloride (E =1.03; E,,=}+0.99) plus 20 mg./ mole of 1,1-di-n-butyl 4,4 'bipyridinium dibromide (E =-0.45; E,= +1.0). After exposure of & second at 0.5 mm. and processing for 1 minute at 27 C. in the fogging developer of Example 3, a high-speed, direct-positive image is obtained.

EXAMPLE 7 To a silver iodobromide emulsion, sulfur-and-goldsensitized as described in Example 1, are added 800 mg. of Dye A of Example 1 per silver mole and the fogging agent 2-methyl [3 (p sulfophenylhydrazono)propyl] benzothiazolium bromide. The emulsion is then coated on a film support, exposed in a Bausch and Lomb spectrograph and developed in a surface developer, Kodak D-19. The observed results show a high-speed reversal image in the 520-600 nm. region.

EXAMPLE 8 A silver halide emulsion similar to that described above in Example 1, containing 800 mg. of Dye A but no fogging agent, is coated on a film support. The coated emulsion is exposed in a Bausch and Lomb spectrograph and placed in Kodak Developer D-19. While immersed in the surface developer, the coating is given an over-all flash to a photoflood lamp for 10 seconds. The flash exposure completely fogs the unexposed areas but not the image areas, thus resulting in a direct-positive image.

EXAMPLE 9 A chemically sensitized silver iodobromide emulsion as described in Example 1 is coated on a film support at 400 mg. of silver/ft To separate emulsion samples are added the following spectral-sensitizing dyes at 800 mg. of dye/ silver mole:

Dye Canhydro-3,9-diethyl-5,5'-dimethoxy-3'-(3 sulfopropyl)thiacarbocyanine Hydroxide (E =1."19;

Dye D5,5'-dichloro-3,3',9-triethylthiacarbocyanine bromide (E =1.06; E,=+.37

Dye E--9-ethyl-3,3'-dimethyl-4,5;4,5' dibenzothiacarbocyanine chloride E=1.09; E =+.58)

Dye Fanhydrous-5,5-dichloro-3,9-diethyl-3-(3 sulfobutyDthiacarboyanine hydroxide (E =l.09;

Dye G2,2',8-trieythlthiacarabocyanine iodide Dye H-3,3',9-triethyl-5,5 dimethoxythiacarbocyanine iodide The above coatings are then exposed on an Eastman 1B sensitometer and developed in the fogging developer described in Example 3. All six coatings exhibit high-speed, direct-positive images.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of the invention.

We claim:

1. A process for producing a positive image comprising (1) imagewise-exposing a silver halide element comprising an unfogged silver halide emulsion which contains an electron-accepting compound having a cathodic halfwave potential more positive than -l.'O and an anodic halfwave potential more positive than +0.4 or a desensitizing concentration of a spectral-sensitizing dye having a cathodic halfwave potential less positive than 1.0 and an anodic halfwave potential more positive than +0.4 and silver halide grains which are substantially free of metal dopants or foreign metal ion occluded therein and have been chemically sensitized on the surface thereof to a level below that which would produce a density of 0.25 when said silver halide emulsion is developed in Kodak Developer DK50 for 6 minutes at 27 C. after imagewise exposure, but which would provide a density of at least 0.3 in a silver halide emulsion of the same grain size not containing an electron-accepting compound or a desensitizing level of a spectral-sensitizing dye when exposed and developed in the same manner, provided said emulsion is coated at a coverage between 300 to about 400 mg. of silver per square foot, and then (2) either (a) developing in a silver halide developer in the presence of a fogging agent or \(b) light-flashing said exposed silver hailde emulsion during development in a silver halide developer.

2. A process according to claim 1 wherein said silver halide is developed in a silver halide developer in the presence of a hydrazine fogging agent.

3. A process according to claim 1 wherein said silver halide is developed in a silver halide developer in the presence of a reactive N-substituted cycloammonium quaternary salt.

4. A process according to claim 1 wherein said silver hailde developers are surface-image developers.

5. A process according to claim 1 wherein said silver halide developers are total-image developers which contain silver halide solvents.

6. A process according to claim 1 wherein said exposed silver halide emulsion is light-flashed during development in a silver halide developer.

7. A process according to claim 1 wherein said silver halide emulsion comprises an electron acceptor having a cathodic halfwave potential more positive than 1.0 and an anodic halfwave potential more positive than +0.4.

8. A process according to claim 1 wherein said silver halide emulsion comprises a desensitizing level of a spectral-sensitizing dye having a cathodic halfwave potential less positive than -l.'0 and an anodic halfwave potential more positive than +0.4.

9. A process according to claim 1 wherein said silver halide grains have been sulfur-and-gold-sensitizecl on the surface thereof which would provide at least a 0.3 log E speed increase in the emulsion in the absence of said electron acceptor or sensitizing dye.

10. A photographic element comprising a support having thereon at least one layer of an unfogged silver halide emulsion which contains an electron-accepting com pound having a cathodic halfwave potential more positive than 1.0 and an anodic halfwave potential more positive than +0.4 or a desensitizing amount of a spectralsensitizing dye having a cathodic halfwave potential less positive than 1.0 and an anodic halfwave potential more positive than +0.4 and silver halide grains which are substantially free of metal dopants or foreign metal ions occluded therein and have been chemically sensitized on the surface thereof to a level below that which would produce a density of less than 0.25 after imagewise exposure when developed in Kodak Developer DK50 for 6 minutes at 27 C. after imageWise exposure, but which would provide a density of at least 0.3 in a silver halide emulsion of the same grain size not containing an electron-accepting compound or a desensitizing level of a spectral-sensitizing dye when exposed and developed in the same manner, provided said emulsion is coated at a coverage between 300 to about 400 mg. of silver per square foot.

11. A photographic element according to claim 10 wherein said silver halide grains are sulf-urand goldsensitized.

12. A photographic element according to claim 10 comprising at least one layer comprising a silver halide fogging agent in Water-permeable association with said silver halide emulsion.

13. A photographic element according to claim 10 which comprises at least one layer containing a fogging agent in water-permeable association with said silver halide emulsion.

14. A photographic element according to claim 13 wherein said fogging agent is a hydrazine compound.

15. A photographic element according to claim 13 wherein said fogging agent is a reactive N-substituted cycloammonium salt.

16. A photographic element according to claim 10 wherein the halide of said silver halide grains is predominantly bromide.

17. A process according to claim 1 wherein said silver halide emulsion contains an electron acceptor having a cathodic halfwave potential more positive than --1.0 and an anodic halfwave potential more positive than +0.4 and a spectral-sensitizing dye.

References Cited UNITED STATES PATENTS 2,456,953 12/1948 Knott et a1. 96-64 2,184,013 12/1939 Leermakers 96-129 NORMAN G. TORCHIN, Primary Examiner W. H. LOWIE, JR., Assistant Examiner US. Cl. X.R. 

